Since an insulated gate bipolar transistor (IGBT) has a high input impedance and a low on-voltage, it is used in a motor driving circuit and the like. However, the IGBT has a tradeoff relation between a withstanding voltage and an on-voltage.
As a result, a variety of methods has been suggested so as to lower the on-voltage while keeping the withstanding voltage high. For example, a structure has been suggested in which an n-type layer (hereinafter, referred to as a ‘carrier accumulation layer’), which has an impurity concentration higher than a drift region and holes are accumulated therein, is formed between a base region and the drift region. According to the structure, the holes are suppressed from reaching an emitter electrode from a collector region, so that the on-voltage can be lowered (for example, refer to Japanese Patent Application Publication No. 2002-353456A).